Auxiliary electrode mediated membrane-free redox electrochemical cell for energy storage

ABSTRACT

The invention provides a membrane-free redox cell utilizing auxiliary electrodes that facilitate fast charging and discharging of anolyte and catholyte for electrochemical energy storage. The anode and cathode chambers are ionically separated, and electrically connected through a conductor joining auxiliary electrodes comprised of a redox material. In use, charging/discharging of the galvanic cell takes place between primary electrodes, and the redox material is immersed in the electrolyte in both anode and cathode chambers.

FIELD

The disclosed innovations are in the field of electrochemistry, relatingto galvanic cells that have an electron conducting connection betweenauxiliary electrodes in place of an ion-conducting or other membrane.

BACKGROUND

Modern energy conversion systems are undergoing phenomenaltransformation to solve the global challenges of addressing climatechange while meeting steadily increasing energy demand [1,2]. Efficientelectrochemical energy conversion systems such as fuel cells and redoxflow batteries operating with zero or low greenhouse gas emissions canhelp mitigate global warming [3,4]. The expensive ionomer material,conventionally used as membranes in these devices, including protonexchange membrane fuel cells (PEMFCs) (˜40% of the total cost of powerdevice) [5], degrades over time and is identified as one of thehindrances to market penetration of these energy technologies [6,7].Membrane-less electrochemical energy storage has also been proposedusing microfluidic channels [8,9], millimeter-sized channels betweenanode and cathode [5,10], gaseous and liquid redox electrolytes [11],and immiscible anolytes and catholytes [12]. All of these advancedelectrochemical cells necessitate anode and cathode compartmentsseparated by ion-conducting membranes or laminar flow of electrolyticfluids for charge separation. Apparently, performance and durabilityissues associated with the ion-conducting membranes remain longstandingissues in fuel cells and batteries.

SUMMARY

An auxiliary electrode mediated membrane-free redox electrochemical cell(AEM²RC) is disclosed herein. The present invention allows the use ofaqueous (acidic/alkaline) or nonaqueous (acidic/alkaline) electrolytesin anode and cathode chambers independent of one another, with electronconducting material connecting the auxiliary electrodes in both chambersduring charging and discharging reactions.

A first cell and electrolyte is in the first compartment, a second celland either a different or the same electrolyte as that of firstcompartment, is in a second compartment. The two separate compartmentsare connected only through an electronically conducting material betweenauxiliary electrodes to form a galvanic cell. The auxiliary electrodemust be a redox active material in a solid or a gel form.

A layer of ion conducting ionomer is coated on auxiliary electrodes toimprove the performance of the cell.

Redox electrolyte material is in the liquid state or is a redox activesolid particle dispersed in supporting electrolyte solution. Duringcharging, anolyte is oxidized and catholyte is reduced. Correspondingauxiliary electrodes undergo reduction and oxidation respectively.

Since, electrons alone are transferred between the two compartments, acombination of aqueous, non aqueous, alkaline and acidic electrolytes ispossible in the second compartment, independent of the nature of redoxelectrolyte in the first compartment.

Since the cathode and anode compartments are physically separate andconnected only by an electron conducting material or metal wire, thecell can operate in a variety of applications. Where anode and cathodeare in close proximity, the cell is practical for battery and energystorage applications. In settings where anode and cathode are widelyseparated, applications might include sensor systems (where oneelectrode compartment is a reference system and the other electrodecompartment is a sensing element or probe). A calibrated referencecompartment with known redox potential measures the redox potential ofan unknown redox electrolyte.

The device may be useful in extracting energy from oxidation of organicmatter in wastewater or fossil fuels, where an oxidant/air cathode iscombined with a subsurface anode cell.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic depiction of an auxiliary electrodemediated membrane-free redox electrochemical cell (AEM²RC),

FIG. 2 shows the constructed prototype cell with auxiliary electrodes(AE), before charging (left panel) and after charging (right panel).

FIG. 3 shows the optical absorption of the anolyte taken at charged anddischarged states as indicated.

FIG. 4 shows XPS spectra of AE1 (left panel) and AE2 (right panel)electrodes, showing the change in oxidation state of elemental Sn3d_(5/2) after charging the AEM²RC.

FIG. 5 consists of two panel showing the configuration of uncoated AE(left panel) and ionomer layer (IL) coated AE pairs (right panel).

FIG. 6 presents the charge-discharge profile of AEM² RC up to 100 cycleswith charge/discharge efficiency on each cycle (top: Ionomer coated AEpair; bottom: uncoated AE pair).

FIG. 7 provides the Nyquist plots of AEM²RC with uncoated and ionomerlayer coated AEs.

FIG. 8 shows the serially connected 4-cell configuration.

FIG. 9 illustrates the charge-discharge profile of 4-cell batteryconnected in-series with uncoated AE pairs.

FIG. 10 presents the redox tower diagram of redox couples compatiblewith acidic and alkaline media.

FIG. 11 illustrating the use of the present invention as a possibleredox potential indicator.

FIG. 12 shows the effect of electrolyte concentration on chargedischarge (left panel) and corresponding impedance behavior of AEsmaterial loading (right panel).

FIG. 13 providing the impedance behavior of individual anode and cathodecompartments with oxidized and reduced AE respectively. Impedancebehavior using SnO₂ (dotted blue) and SnO (solid red) as counterelectrodes. Cathode (V³⁺/Sn²⁺ pair) impedance is higher at both high(inset (c)) and low frequencies.

FIG. 14 includes two panels, illustrating (a) an all-aqueous electrolyteconfiguration and (b) AEM²RC configured with a nonaqueous and aqueouselectrolyte in the anode and cathode compartment respectively.

FIG. 15 representing the schematic of concentrically placed porousprimary and auxiliary electrodes for increasing the electrochemicalreaction surface area.

FIG. 16 representing the schematic of stack description of AEM²RC for10-12 kW power generation.

FIG. 17 shows the hybrid AEM²RC with 10 mM mixed model quinones (1:1:1of acenaphthenequinone, phenanthrenequinone and 1,2-dihydroxyquinone) in100 mM tetrabutylammomium hydroxide in NN′-dimethylformamide in anodeand aqueous 100 mM iodine/100 mM KOH in cathode. Here, the auxiliaryelectrode pair used was Ni³⁺/Ni²⁺.

FIG. 18 shows cyclic voltammogram of 10 mM mixed model quinones (1:1:1of acenaphthenequinone, phenanthrenequinone and 1,2-dihydroxyquinone) inN,N″ dimethylformamide with 100 mM tetrabutylammomium hydroxide in anodequinone and (c) 1,2-dihydroxyquinone in N,N″ dimethylformamide with 100mM tetrabutylammomium hydroxide (red) cathode Iodine (blue).

FIG. 19 shows the cell capacity of AEM²RC during charge-discharge cyclefor given electrode area of 2.25 cm².

FIG. 20 demonstrates an improved coulombic efficiency fromcharge-discharge characteristics for 100 cycles of (top) all-aqueousvanadium redox cell and (bottom) non-aqueous anode and aqueous cathode.

FIG. 21 shows (a) Polycyclic aromatic hydrocarbon (PAH) based quinonesused in this study, (b) The proposed change in the structure ofquinone-like molecule with charging reaction that may lead to thesharpening of NMR signal (c) ¹H NMR spectra of mixed quinones from anodeafter charging and discharging. NMR scans were recorded using at 400 MHzfrequency with 50% sample: 50% CDCl₃.

DETAILED DESCRIPTION

A separate chamber electrochemical redox cell is disclosed herein,adapted to store and release electrochemical energy, where the anode andcathode chambers are connected by auxiliary electrodes (AEs) throughmetal wire/electron conducting medium (FIG. 1). The constructedprototype is shown in FIG. 2. The proposed half-cell electrochemicalredox reactions at anode, cathode and AEs are presented in eqns. (1-2).

The overall potential of AEM²RC is:E _(Overall) =E _(A) +E _(C)=(E _(a) ⁰ −E _(AE1) ⁰)+(E _(c) ⁰ −E _(AE2)⁰)  (3)

where E_(A) and E_(C) represent half-cell potentials of anode andcathode side reactions [13]. E_(A) is the potential difference betweenanode (E_(a) ⁰) and AE1 in the anode chamber, and E_(C) is the potentialdifference between cathode (E_(c) ⁰) and AE2 in the cathode chamber(equation (3)). E^(o) is the standard reduction potential of the redoxcouple under standard temperature (T=298.15 K) and pressure condition.The redox state switching accepts and releases electrons at the AEs.

As just one example of a practical configuration, starting with 100 mMvanadyl sulfate solution in both chambers, where vanadium exists in 3+and 4+ oxidation states in equal amounts, during charging VO²⁺ (V⁴⁺) isoxidized to VO₂ ⁺ (V⁵⁺) at the anode and V³⁺ ions are reduced to V²⁺ atthe cathode. The vanadium electrolyte in the anode compartment was takenin diluted small quantity at the end of charge, discharge, and chargecycles for analysis. The presence of VO₂ ⁺ is supported by the opticalabsorption spectra of the anolyte in FIG. 3. The corresponding AEsundergo reduction (Sn⁴⁺ to Sn²⁺ at AE1) and oxidation (Sn²⁺ to Sn⁴⁺ atAE2) reactions. This is confirmed by the XPS spectra of the electrodesAE1 and AE2 in FIG. 4. The proposed redox electrochemical cell, withouta membrane between the anode and cathode requires suitable AEs. (i.e.,reduced form in the catholyte chamber and the oxidized form in theanolyte chamber.) A stoichiometrically higher amount of AE loadingcompared to the mass of the redox active electrolyte is preferred toovercome concentration dependent limitations (FIG. 5). The twohalf-cells when connected form a complete cell (Eqn. 3) with a totalopen circuit voltage (OCV), i.e., (−0.25−0.14)+(1−0.14)=0.5 V. The OCVof the auxiliary electrode mediated membrane-free redox electrochemicalcell (AEM²RC) redox cell was recorded for about 18 h and was found to bestable. The overall charging and discharging reactions are:

Charging at 1.8 V and deep discharging at 0 V were performed to ensurecyclability as shown in FIG. 6. With cell charging, higher opticalabsorption (λ_(abs)) near 250 nm indicated a higher concentration of VO₂⁺(V⁵⁺) species, with discharging leading to lower optical absorption dueto fewer VO₂ ⁺ species compared to the charging cycle [14].

XPS results (FIG. 4) revealed the existence of significant proportions(23%) of Sn²⁺ in the anode compartment AE1, which was initially 100%Sn⁴⁺. The constructed AEM²RC successfully undergoes charging/dischargingcycles but if left in the charged state starts decaying rapidly. Thiscould be mainly due to the fast charge-transfer by direct contact ofcharged and discharged vanadium ions with the respective AE redox metalcenters.

Mitigation of this problem was achieved by the novel route of coatingthe AEs with an ionomer film as shown in FIG. 7. Two redox cells(|V^(4+/5+)/Sn^(4+/2+)||Sn^(2+/4+)/V^(3+/2+)|), in-series with ionomercoated AEs were found to exhibit higher charge/discharge efficiency,related to the vanadium ions isolation from the Sn redox centers (FIG.7). The impedance response of the AEM²RC on a Nyquist plot was anincomplete semi-circle (FIG. 8), with a high-frequency intercept of ˜7Ω,corresponding to the solution resistance. Attributing the semi-circularimpedance response to the electrode processes, it is evident that theelectrode polarization resistance for ionomer coated AEs are higher thanuncoated AEs. Larger semicircle on the Nyquist plot for the cell withionomer coated auxiliary electrodes indicates an increased capacitivebehavior with ionomer coating. This suggests that the charged speciesare well separated by ionomer coating, attributes to the increasedcharge discharge efficiency. The electrode resistance of the AEM²RC withionomer layer coated AEs is higher compared to the cell with uncoatedAEs. The individual chamber's impedance behavior was studied and it wasfound that the cathode compartment impedance at high and low frequencyis higher than that of the anode compartment, as shown in FIG. 9.

The essential advantage of the demonstrated membrane-free, AEM²RC,involving separate anode and cathode chambers, is to couple spatiallyseparated oxidation and reduction processes, which is not possible usingconventional flow cells with membranes. The degradation issues and costassociated with the membrane are eliminated in the proposed design. Arange of redox electrolytes with high cell voltage can be selected basedon the reduction potentials in FIG. 10, to achieve high energy densitythrough the novel mechanism described in this work. Since only electronsare transferred between the chambers, a variety of different (alkalineacidic or aqueous/non-aqueous) redox electrolytes can be used in anodeand cathode chambers respectively, even if they are physicallyincompatible.

The sensor application also uses the same principle as that of abattery, except a known redox electrolyte with redox potential (Er) inthe reference chamber is gauged against an unknown redox electrolytewhose redox potential is (Ex) using the modified from of Eqn. (3). Theschematic of redox potential sensor using present invention is providedin FIG. 11)E _(X) ⁰ =E _(Overall) −E _(R) ⁰ +E _(AE1) ⁰ +E _(AE2) ⁰  (5)

EXAMPLES

The scaled up prototypes of the AEM²RC in a 4-cell configuration wasconstructed in 20 mL and 200 mL chamber volumes as per the schematicpresented in FIG. 12. Initially, the scaled up prototypes wereconstructed with uncoated auxiliary electrode pairs whosecharge-discharge profile is shown in FIG. 13.

While the constructed all aqueous electrolyte design is presented inFIG. 14 (left), the design was extended further to accommodate aqueousand nonaqueous electrolytes in separate individual chambers. Theconstructed lab scale prototype with non-aqueous anode electrolyte(Anthraquinone sulfonate (AQS) in N—N′ dimethyl formamide (DMF)) andaqueous vanadium based electrolyte is shown in FIG. 14 (right). Herein,quinone (and/or aromatic ketone) fractions derived from crude oil [15],or other sources, can be used as electrolytes in aqueous or nonaqueousforms. These types of chemical species are particularly abundant in“resin” and “asphaltene” fractions of heavy, (bio)degraded oils, such asCanadian oil sands/bitumen [16-19]. Electrolytes can be of varied formsand consist of multiple or single components derived from a variety ofsources.

The efficiency of the energy conversion could be increased when tubularporous electrodes with diameter (D), length (L) and thickness (tel) areemployed in the electrolyte chambers as shown in FIG. 15, the obtainablepower can be calculated as follows:

Geometric area of the electrode, A=πDL=(D=40 cm; L=50 cm) ˜6200 cm².

Active region thickness t_(el)=1 cm

Volume of porous electrode=πDL×t_(el)=6200 cm³

Surface area available,

${\frac{S}{V} = {\sim \frac{6\left( {1 - ɛ} \right)}{d_{charatersitic}}}};$${d_{charatersitic} \sim {{pore}\mspace{14mu}{diameter}}} = {{1\mspace{14mu}{\mu m}} = {{10^{- 4}\mspace{14mu}{{cm}.\frac{S}{V}}} = {\sim {\frac{6\left( {1 - {0.3}} \right)}{10^{- 4}}\frac{{cm}^{2}}{{cm}^{3}}}}}}$

Surface area available=4.2×10⁴ cm⁻¹

$\begin{matrix}{{{Total}\mspace{14mu}{surface}\mspace{14mu}{area}\mspace{14mu}{of}\mspace{14mu}{the}\mspace{14mu}{electrode}} = {4.2 \times 10^{4}\mspace{14mu}{cm}^{- 1} \times 6200\mspace{14mu}{cm}^{3}}} \\{= {\sim {260 \times 10^{6}\mspace{14mu}{cm}^{2}}}} \\{= {\sim {2.60 \times 10^{4}\mspace{14mu}{m^{2}.}}}}\end{matrix}$

Total current,

$i_{tot} = {\sim {{i\left( \frac{A}{{cm}^{2}} \right)} \times {total}\mspace{14mu}{area}}}$

Power=i×V

Based on reasonable assumptions, if 0.5 M electrolytes based on Zn andAQS electrolyte systems was used in a system whose redox potentials arepresented as follows,Zn²⁺(aq)+2e ⁻

Zn(s); E ₀=˜−0.76 V[AQS]_(Ox)+H⁺ +e ⁻

[H−AQS]_(Red) ; E ₀=˜0.057 VWithout considering the voltage loss at the AE pair reactions, from theenergy density calculations, it may take approximately 91 liters ofelectrolyte to store/discharge 1 kW of power.

${{E\left( {W\text{/}L} \right)} = \frac{nCFV}{2}};{{{If}\mspace{14mu} n_{c}C_{c}} = {n_{a}C_{a}}};{2*{0.5}}$${E\left( {W\text{/}L} \right)} = {\frac{1 \times 2{6.8} \times {0.8}17}{2} = {\sim {11\frac{W}{L}}}}$˜91 L of 0.5 M electrolytes could generate 1 kW.

Alternate auxiliary electrode materials include SnO₂/SnO, Fc⁺/Fc pairsfor acidic electrolytes such as vanadium in diluted sulfuric acidsolution, or NiOOH/Ni(OH)₂ pairs for alkaline electrolytes such as AQSand Zn in diluted potassium hydroxide solutions.

Alternate electrolytes, include: aqueous electrolytes, such as solutionsof iron, zinc, manganese, chromium, AQS, Benzoquinone (BQ), orferrocyanide; and non-aqueous electrolytes, such as ferrocene,anthraquinone, AQS, Anthraquinone 2,6 disulfonate (AQDS), fluorenone,and other types of organic, and organometallic redox active species.

Alternate primary electrode materials include platinum on carboncatalyst, for example with a loading of 0.25 mg/cm² coated on 5%polytertrafluroethylene (PTFE) wet-proofed carbon cloth (as primaryelectrodes for liquid electrolytes). Alternately, carbon paper can beused in liquid electrolytes with vanadium, ferrocene, zinc, AQS, AQDS.Carbon felt/foam can be used with semisolid redox electrolytes such aszinc, MnO₂ to increase the contact area.

Sample Energy Density Calculations Based on Non-Aqueous Anode andAqueous Cathode Redox ElectrolytesI₃ ⁻+2e ⁻→3I⁻; E₀=0.536 V  Cathode:[Q]_(Ox)+H⁺+e⁻

[Q]_(Red); E₀=˜−1.0 V  Anode:

${{E\left( {{Wh}\text{/}L} \right)} = \frac{nCFV}{2}};{{{If}\mspace{14mu} n_{c}C_{c}} = {n_{a}C_{a}}};{2*{0.5}}$${E\left( {{Wh}\text{/}L} \right)} = {\frac{1 \times 26.8 \times 1.043}{2} = {\sim {11\frac{Wh}{L}}}}$

˜72 L of 0.5M electrolytes could generate 1 kWh.

˜720 L or (170 Gal) of 0.5M electrolytes could generate 10 kWh.

TABLE 1 List of redox electrolytes, auxiliary electrode pair and primaryelectrode combinations Redox electrolyte Auxiliary electrode pairPrimary electrodes All vanadium SnO₂/SnO Pt/C coated on carbon Zn/Fecloth, plain carbon paper, AQS/Fe plain carbon cloth BQ/Zn BQ/Zn Fe/CrAll vanadium NiOOH/Ni(OH)₂ MnO₂ coated on carbon, AQS/Fe plain carbonpaper, plain BQ/Zn carbon cloth BQ/Zn Fe/Cr Quinone/Iodine Zincparticles-quinone SnO₂/SnO Porous carbon foam, based electrolytes carbonfelt etc. MnO₂ particles-quinone Zinc particles-quinone NiOOH/Ni(OH)₂Porous carbon foam, based electrolytes carbon felt etc.

In some embodiments, the redox electrolyte may be circulated throughporous concentrically placed primary and auxiliary electrodes, forexample so as to increase electrochemical surface area for higherefficiency. The redox electrolyte may for example be circulated throughporous concentrically placed primary and auxiliary electrodes separatedby a chemically inert insulating mesh. In some embodiments, one of theredox electrolytes may be a gel-type electrolyte with a known redoxpotential situated between the primary and auxiliary electrodes. In analternative embodiment, an end of a primary and auxiliary electrode maybe used as a sensing probe, immersed in a redox electrolyte with anunknown redox potential, thereby adapting the device for use as a redoxvoltage sensor.

Chemicals and electrodes. For the exemplary embodiments described above,Vanadyl sulfate 97% and anthraquinone-2 sulfonate (ACS grade from SigmaAldrich) were used to prepare the electrolyte solutions. 37% sulfuricacid stock solution (ACS grade from Sigma Aldrich), was used to preparesupporting electrolyte. For non-aqueous studies, N—N′ dimethylformamidewas used as solvent. Tin(II) oxide (SnO, particle size >60 μm) and Tin(IV) Oxide (SnO₂, particle size >10 μm) powders from Alfa Aesar,polytetrafluoroethylene (PTFE) dispersion (30 wt. %) from E.I. dupont DeNemours & Co. Inc., graphite powder, isopropyl alcohol and water wereused in making the slurry for the preparation of auxiliary electrodepair. The procedure can be found elsewhere [20]. The loading of metaloxides was 60 mg/cm² along with 10 wt. % conducting graphite powder and15 wt. % PTFE binder.

Electrochemical characterization. Cyclic voltammetry (CV) of half-celland full cell devices was performed using a Bio-logic VSP 300potentiostat. Glassy carbon was used as a working electrode, SnO andSnO₂ were used as as counter electrodes to ease electron acceptance andrelease in the custom made half-cells with respect to a referencehydrogen electrode (RHE) comprises of Pt foil immersed in 0.5 M sulfuricacid with bubbling hydrogen gas at 1 atm pressure. Typical CVexperiments were performed at a scan rate of 20 mVs⁻¹. Electrochemicalimpedance spectroscopy (EIS) experiments was carried out in thefrequency range of 1 MHz-1 Hz at open-circuit conditions with a 10 mV acamplitude. The EIS data was analyzed via equivalent circuit fittingusing EC-lab® software (Bio-logic, France). Charge-discharge cycles (1.8V/0 V) were performed using galvanostatic cycling with potentiallimitation (GCPL) technique in EC-Lab software. Cyclic voltammetrystudies of redox electrolytes were carried out using three-electrodeconfiguration in non-aqueous media. Large potential window scans wereperformed with −2 V to +1 V vs. Ag/Ag+ non-aqueous reference electrode(CH instruments). The working electrode is 3 mm dia. glassy carbon rodand counter electrode is a piece of platinized platinum.

UV-VIS characterization. The electrolyte solution absorption spectra incharged and discharged states were obtained using a Varian Cary 300 Biodouble beam UV-Vis spectrophotometer. The absorption spectrum wererecorded from 200 nm to 800 nm. The electrolytes from both chamber werediluted to avoid the saturation of optical detector.

XPS characterization. Room-temperature XPS experiments were performed atnanoFAB facility (University of Alberta) using Kratos Axis spectrometerwith monochromatized Al Kα (hu=1486.71 eV). The spectrometer wascalibrated by the binding energy (84.0 eV) of Au 4f7/2 with reference toFermi level. The pressure of analysis chamber during experiments isbetter than 5×10⁻¹⁰ Torr. A hemispherical electron-energy analyzerworking at the pass energy of 20 eV was used to collect core-levelspectra while survey spectrum within a range of binding energies from 0to 1100 eV was collected at analyzer pass energy of 160 eV. Chargeeffects were corrected by using C 1s peak at 284.8 eV. A Shirleybackground was applied to subtract the inelastic background ofcore-level peaks. Non-linear optimization using the Marquardt Algorithm(Casa XPS) was used to determine the peak model parameters such as peakpositions, widths and peak intensities. The model peak to describe XPScore-level lines for curve fitting was a product of Gaussian andLorentzian functions (GL (50)). UPS was performed at nanoFAB facilityusing Kratos Axis Ultra spectrometer. UPS was measured with He I source(hv=21.2 eV). The sample was −10 V bias on. The power for UPS was 3kV×20 mA (60 W). Compositions were calculated from the survey spectrausing the major elemental peaks and sensitivity factors provided by thedatabase. CASA XPS was used for component analysis to fit the spectra ofC1s with peaks related to different chemical bonds. A CasaXPS (academic)program was used to analyze the data. Standard reduction potentials ofredox active elements that are usable in the AEM²RC is presented in theredox tower diagram in FIG. 10 [21-23].

Nuclear magnetic resonance spectra studies. NMR instrument from BrukerAVIII-400“RDQ” BBFO Probe Ultrashield Magnet were used in this study.NMR studies were carried out by mixing 50 vol % sample with 50 vol %CDCl₃ (Sigma Aldrich) as proton source for non-aqueous media.

Charging and Discharging Reactions in Conventional Vanadium Redox FlowBattery¹³

System Level Description for 10 kW AEM²RC

The system consists of two storage tanks for anolyte and catholyte forstoring and retrieving electrochemical energy as described in FIG. 16.

Each cell consists of a pair of primary electrodes and a pair ofauxiliary electrodes.

Each cell is connected in series to build-up the voltage.

The DC current is fed to the AEM²RC where the electrolytes are convertedto high energy fluids. To better utilize the electrolyte, circulatorpumps in both tanks need to be operated at regular intervals.

The primary electrode is used to charge and discharge the cell, duringcharging, anolyte is electrochemically oxidized and catholyte iselectrochemically reduced.

Auxiliary electrodes are used to transport electron when the auxiliaryelectrodes undergo counter electrochemical reactions respectively.

During discharging, the applied voltage and current electrochemicallyreduce the anolyte and oxidizes the catholyte to generate electricaloutput.

When electricity is needed, the chemical energy stored in high energyelectrolytes are converted to DC power.

Separate tanks can be used when we need power-on-demand, so thatcirculating the electrolyte leads to power generation. This also avoidsome minor self-discharge.

Self-discharging problem can be avoided by electrically disconnectingthe anode and cathode after charging in the resent design.

Features

Separate tank design allows power on demand and provision toelectrically disconnect anode and cathode chamber to reduceself-discharge problem.

Electrochemical charging and discharging are spontaneous in AEM²RC.Hence, they are exothermic.

During urgent power demand and charging, the incoming DC power can befed directly to the output converter to avoid the delayed response ofthe AEM²RC. One the power is surplus, the electrolytes can be charged tostore energy.

TABLE 2 Approximate cost and performance characteristics (Scaled-up for10-12.5 kW) Item Description Cost, in C$ Foot print 2.5 × 2.5 m². Notincluded Area of each electrode (25 × 25) 5000 cm² (0.5 m²) Primaryelectrode Catalyst coated carbon cloth 15000 electrode (50 m²) C$300/m²Auxiliary electrode Ni(OH)₂ 7.5 kg each on SS mesh @ C$5/kg 50 Auxiliaryelectrode NiOOH 7.5 kg each on SS mesh @ C$10/kg 100 Stainless steelmesh 50 m² @ C$15/m² 750 Concentration of the 500 mM (Iodine andquinone) electrolyte Storage tank 1000 L PVC containers × 2 500 Tubing &plumbing 10 meters @ C$10/m; 100 Anolyte 0.5 M/5M quinone 4250 (9 kg ofquinone|C$25/kg) 2250 (975 kg of TBAH|C$1.5/kg) 1000 (NN′dimethylformamide 750 liter| C$1000 for 1 ton) Catholyte 0.5 M/5M Iodine7000 (95 kg of iodine|C$60/kg) 5700 (62.25 kg of KI|C$0.75/kg) 60(105.19 kg of KOH|C$1.5/kg) 170 (H₂O 750 liter|C$100 for 1000 liters)Flow rate of electrolyte Circulation at 10 slpm (Two pumps @ C$1000)1000 Storage volume 750 liters × 2 DC-DC converter + battery For 10 kWh(C$350 + C$1000) = C$1350 1350 management system (BMS)Cables/connections/fixtures C$1000 1000 Charging time 5-7 hours Numberof cells 50 Open circuit voltage 50.0 V Maximum charge voltage 80.0 V to90.0 V Minimum voltage on 30.0 V discharge Maximum charge current 40.0 A(@ 8.0 mA/cm²) Maximum discharge current 25.0 A (@ 5.0 mA/cm²)(continuous) Rated capacity for 8-10 hours 10-12.5 kWh Power out put DCTotal 31100 Service Life 20,000 hours <0.25/kWh

System Level Outlook

The energy density of the proposed system is based on the volume of theredox electrolytes involved, reduction potentials of the redox couples,concentration of the redox electrolytes, number of electrons involved inthe redox reaction. The proposed system generates only DC power throughelectrochemical energy conversion. Hence, a DC-DC converter is requiredto convert the output power from the redox cell. The current technologyrequired only abundant and cheaper materials than conventional redoxflow battery, which brings down the cost of the system considerably lessthan that of flow battery system with expensive membrane and metal basedredox system. Hence, metal-free redox electrolytes are tested in thesecond phase of the project. The energy density of the AEM²RC depends onthe volume of the electrolytes and power density depends on thedimensions of the electrodes. Conveniently, here energy and power isdecoupled in the system similar to redox flow battery system.

Advantages

The flow rate, electrode area, storage tank capacity, DC-DC converter,service life, etc., are similar to that of conventional redox flowbattery, except that, we have eliminated the use of ion-exchangemembrane. Instead of this, we have incorporated auxiliary electrodes,which has following advantages.

No membrane used in the system, hence, the cost of the membrane iseliminated.

Mass-transport restriction across the membrane is eliminated. Hence,flexible electrolytes can be used in anode and cathode chamber.

No separate storage tanks required. Stack and electrolyte storage can beused in one container for anode and cathode.

Agitation at regular interval is sufficient. No constant electrolytecirculation is required. Hence, pumping loss can be kept to a minimum.

Zero pressure gradient is observed due to the absence of bipolar platesor flow channel. Hence, pumping power is significantly lower thanconventional redox flow battery.

Previous design of AEM²RC was tested using all-aqueous vanadium basedredox electrolyte. Owing to the cost and less abundant nature, vanadiumis often not desired candidate for redox electrolyte application. Highconcentration of electrolyte is required to realize high energy density,which necessitates the use of low pH acidic supporting electrolyte. Highconcentration electrolytes also have crystallization issues and thus hasvery limited operational temperature window. Higher concentration ofelectrolyte may require careful engineering of electrode surface forimproved wettability. The supporting electrolyte was 1 M sulfuric acid,which leads to many corrosive issues of the components used. Due to themajor problems listed above, non-metallic and non-aqueous based redoxelectrolytes are often preferred. Organic redox electrolyte is used as anegative reactant with high solubility in non-aqueous media with reducedcost per kWh compared to vanadium is often investigated.

Here, we propose a non-aqueous redox electrolyte with a mixture ofquinone based molecules. Lab-scale experiments were demonstrated asdepicted in FIG. 17.

A mixture of three different polycyclic aromatic hydrocarbon (PAH)quinones (Acenapththenequinone, Phenanthrenequinone, and1,2-dihydroxyanthraquinone) were tested. Iodine (I₃ ⁻/I⁻) was used ascatholyte in alkaline aqueous media, where the redox behavior ispresented in FIG. 18.

The capacity retention of AEM²RC is shown from the charge-dischargecharacteristics shown in FIG. 19.

The cyclability study of the AEM²RC demonstrated for 100 cycles revealsthat AEM²RC with the hybrid reactants had an increased coulombicefficiency that is ˜2.5 time higher than the all-aqueous reactants aspresented in FIG. 20.

The chemical structure of quinones used in this study as shown in FIG.21(a). Upon redox (charging) reaction as proposed in FIG. 21(b), thequinone aromatic signals in NMR spectra sharpen, which are identifiedwith an asterisk as shown in FIG. 21(c). This sharpening may be due tothe loss of the aromatic hydroxyls with the oxidation reaction whichhave become quinoid as shown in the NMR spectrum.

The redox studies exhibited an overall single redox potential for thesemixed quinone electrolyte in NN′-dimethylformamide withtetrabutylammonium hydroxide as supporting electrolyte.

The auxiliary electrode pair in Ni(OH)₂/NiOOH.

Since AEM²RC operates without any mass transport restrictions, Thehybrid design of non-aqueous anode and aqueous cathode is possible withthe opportunity of replacing expensive metal electrolytes with cheaperorganic electrolyte. The alkaline electrolyte on cathode side mitigatescorrosion issues associated with the acidic electrolyte. Non aqueousmedia increases the solubility limit of anolyte thus an increased energydensity is possible.

TABLE 3 Application space and cost metrics 10 kWh conversion RequiredCost of system Efficiency infrastructure 10 kWh, C$ Area required for 10kWh <20% 1000 sqft 0.39 from Solar cells [24] illumination Hydrogenrequired for 40-50% ~550 grams 2.00 10 kWh from fuel cells of hydrogen[25, 26] Location specific area ~50% ~10 m/s wind 1.10 required for 10kWh from flow windmill [27] Flow and height ~80% 2.5 m net head 11.4requirement for 10 kWh water that flows from hydro [28] at 600liter/second.

Real Application Space Scenario

Deployment in Solar Fields

Because of the geographical location, Southern Alberta always receives adecent amount of sunlight for 8-10 months of the year [29]. Alberta hasthe second highest potential to produce solar energy in all of Canada,receiving more solar irradiation than any other province or territoryother than Saskatchewan. According to data from National ResourcesCanada, the average solar system in Alberta can produce 1276 kWh ofelectricity per kW of solar panels per year. Calgary-based PerimeterSolar located about 125 kilometers south of Calgary, is building 130 MW,a $200-million solar facility. The AEM²RC can be linked to the solarpanels to generate power when sun shines.

Hydrogen Gas from Oil Well Converted to Energy

Natural gas resource is quite important to the economic development ofthe province, where Alberta produced 10.5 billion cubic foot/day ofnatural gas in 2018. Contracted use of hydrogen from oil well can bedone with the excess of flared gas. Local legislations also gets tighterfor gas flaring at oil fields in some locations in North America. Asimilar case can be planned in the Superb oil field in Saskatchewan,Canada, where hydrogen gas is taken out from the oil well by injectingsteam and air leaving the CO₂ underground. Proton technologies use theirmembrane to separate hydrogen gas, but the fuel cell employed couldproduce power to be stored in the AEM²RC.

Windmill Energy Storage

Alberta ranks third in Canada with an installed wind energy capacity of1,685 MW. Regions with an average annual wind speed of at least 6-7 m/s(22-25 km/h) or greater at a height of 80 m above the ground (the hubheight) are considered potentially economically viable areas forcommercial wind energy development. Many best suitable sites are foundin the southern part of Alberta. Wind farms such as Oldman1, Oldman2,Old elm, Sharp hills, and Windy point wind farms generate nearly 700 MWof energy of which part of the energy can be stored and supplied duringpeak shaving time.

Hydroelectric Energy Storage

The hydroelectric potential of the province lies mostly in theAthabasca, Peace and Slave River basins. The remaining is in the RedDeer River basin and the North and South Saskatchewan River basinswithin the southern part of the province. Combining, they have thepotential to generate 42000 GWh/year. Hydroelectric power is sitespecific and the river corridors are important habitat for terrestrialand aquatic ecosystem. Therefore, storing the energy and using it at thespot eliminates the need of power transmission lines without disturbingthe environment. TransAlta and Atco power are the main players ingenerating hydroelectric power in Alberta, operating mainly from Southof Alberta, totaling nearly 900 MW of power.

Over the past 10 years, Albertans were paying between $48 and $90/MWhfor the coal-fired electricity. The deployment of such innovativetechnology creates an independency from fossil-based energy and reduceGHG emission.

INCORPORATED REFERENCES

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Although various embodiments of the invention are disclosed herein, manyadaptations and modifications may be made within the scope of theinvention in accordance with the common general knowledge of thoseskilled in this art. Such modifications include the substitution ofknown equivalents for any aspect of the invention in order to achievethe same result in substantially the same way. Terms such as “exemplary”or “exemplified” are used herein to mean “serving as an example,instance, or illustration.” Any implementation described herein as“exemplary” or “exemplified” is accordingly not to be construed asnecessarily preferred or advantageous over other implementations, allsuch implementations being independent embodiments. Unless otherwisestated, numeric ranges are inclusive of the numbers defining the range,and numbers are necessarily approximations to the given decimal. Theword “comprising” is used herein as an open-ended term, substantiallyequivalent to the phrase “including, but not limited to”, and the word“comprises” has a corresponding meaning. As used herein, the singularforms “a”, “an” and “the” include plural referents unless the contextclearly dictates otherwise. Thus, for example, reference to “a thing”includes more than one such thing. Citation of references herein is notan admission that such references are prior art to the presentinvention. Any priority document(s) and all publications, including butnot limited to patents and patent applications, cited in thisspecification, and all documents cited in such documents andpublications, are hereby incorporated herein by reference as if eachindividual publication were specifically and individually indicated tobe incorporated by reference herein and as though fully set forthherein. The invention includes all embodiments and variationssubstantially as hereinbefore described and with reference to theexamples and drawings.

The invention claimed is:
 1. A galvanic cell comprising: ionicallyisolated cathodic and anodic half cells, the cathodic half cellcomprising a primary cathode and an auxiliary anode in a cathodicelectrolyte, the anodic half cell comprising a primary anode and anauxiliary cathode in an anodic electrolyte, the cathodic electrolytebeing ionically isolated from the anodic electrolyte; the primarycathode comprising a primary cathode terminal, and the primary anodecomprising a primary anode terminal, the primary cathode and anodeterminals being electrically connected through an external storage anddischarge mechanism; and the auxiliary anode being electrically coupledto the auxiliary cathode by an electron conductor, the cathodic halfcell being thereby electrically coupled to the anodic half cell throughthe electron conductor to form a reversible circuit with reversible halfcell reactions that alternatively mediate electrochemical energy storagereactions and electrochemical energy discharge reactions.
 2. Thegalvanic cell of claim 1, wherein the cathodic electrolyte comprises V³⁺and V²⁺, and wherein the anodic electrolyte comprises VO²⁺ and VO²⁺. 3.The galvanic cell of claim 2, wherein to mediate electrochemical energystorage by the electrochemical energy storage reactions, VO²⁺ in theanodic electrolyte is oxidized at the primary anode to form VO²⁺, andV³⁺ in the cathodic electrolyte is reduced at the primary cathode toform V²⁺.
 4. The galvanic cell of claim 3, wherein to mediateelectrochemical energy discharge by the electrochemical energy dischargereactions, VO²⁺ in the anodic electrolyte is reduced at the primaryanode to form VO²⁺, and V²⁺ in the cathodic electrolyte is oxidized atthe primary cathode to form V³⁺.
 5. The galvanic cell of claim 4,wherein the cathodic electrolyte and the anodic electrolyte are vanadylsulfate solutions in an acidic supporting electrolyte.
 6. The galvaniccell of claim 5, wherein the auxiliary anode and/or auxiliary cathodecomprises: a redox metal oxide or a mixed metal oxide; or, wherein theauxiliary anode comprises tin IV oxide (SnO₂); or, wherein the auxiliarycathode comprises tin II oxide (SnO); or, wherein the auxiliary anodeand/or auxiliary cathode comprise a composite electrode comprising acarbonaceous substrate material; or, wherein the auxiliary anode and/orauxiliary cathode comprise an ionomer film coating covering theauxiliary anode and/or auxiliary cathode; or, wherein the auxiliaryanode and/or auxiliary cathode comprises a redox gel material.
 7. Thegalvanic cell of claim 6, wherein the auxiliary anode comprises tin IVoxide (SnO₂), and the auxiliary cathode comprises tin II oxide (SnO),wherein to mediate electrochemical energy storage by the electrochemicalenergy storage reactions, a portion of the tin IV in the auxiliary anodeis reduced to tin II, and a portion of the tin II in the auxiliarycathode is oxidized to tin IV.
 8. The galvanic cell of claim 7, whereinto mediate electrochemical energy discharge by the electrochemicalenergy discharge reactions, a portion of the tin II in the auxiliaryanode is oxidized to tin IV, and a portion of the tin IV in theauxiliary cathode is reduced to tin II.
 9. The galvanic cell of claim 6wherein the ionomer film coating comprises an ion conductive materialthat is an electronic insulator; a perfluorosulfonic acid (PFSA) ionomerdispersion; a polyethylene oxide (PEO); or, a polypropylene oxide (PPO).10. The galvanic cell of claim 6, wherein the redox gel materialcomprises an ion conducting and electron conducting media supported on asubstrate or a porous matrix; or a ferrocene (Fc) based gel; or an ionicliquid based gel; or, a redox active polymer.
 11. The galvanic cell ofclaim 10, wherein the redox active polymer comprises a conjugatedpolymer backbone.
 12. The galvanic cell of claim 11, wherein theconjugated polymer backbone comprises a poly aniline (PANI); a poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) and/orwherein the conjugated polymer backbone comprises a redox active groupsubstituent.
 13. The galvanic cell of claim 12, wherein the redox activegroup substituent is a quinone, imide, carbazole, or ferrocene.
 14. Thegalvanic cell of claim 1, wherein the cathodic electrolyte is circulatedfrom a cathodic electrolyte storage tank through the cathodic half cell,and the anodic electrolyte is circulated from an anodic electrolytestorage tank through the anodic half cell.
 15. The galvanic cell ofclaim 1, wherein the cathodic and anodic electrolytes comprise a redoxelectrolyte pair, the auxiliary anode and auxiliary cathode comprise anauxiliary electrode pair, and the primary cathode and primary anodecomprise a primary electrode pair, and: a) the redox electrolyte paircomprises: i) vanadyl species, or ii) zinc (Zn) and iron (Fe) species,or iii) anthraquinone sulfonate species (AQS) and Fe species, or iv)benzoquinone (BQ) and Zn species, or v) Fe and chromium (Cr) species;the auxiliary electrode pair comprises SnO₂ and SnO; and the primaryelectrode pair comprises: i) platinum on carbon catalyst (Pt/C) coatedon carbon cloth, or ii plain carbon paper, or iii) plain carbon cloth;or b) the redox electrolyte pair comprises: i) vanadyl species, or ii)AQS and Fe species, or iii) BQ and Zn species, or iv) Fe and Cr species,or v) quinone and iodine species; the auxiliary electrode pair comprisesNiOOH and Ni(OH)₂; and the primary electrode pair comprises: i) MnO₂coated on carbon, or ii) ii) plain carbon paper, or iii) plain carboncloth; or, c) the redox electrolyte pair comprises a quinone-basedelectrolyte comprising; i) zinc particles; or ii) MnO₂ particles; theauxiliary electrode pair comprises SnO₂ and SnO; and the primaryelectrode pair comprises porous carbon foam or carbon felt; or, d) theredox electrolyte pair comprises a quinone-based electrolyte comprisingzinc particles; and, the auxiliary electrode pair comprises NiOOH andNi(OH)₂; and, the primary electrode pair comprises porous carbon foam orcarbon felt.
 16. The galvanic cell of claim 15, wherein the redoxelectrolyte is circulated through porous concentrically arranged primaryand auxiliary electrode pairs.
 17. The galvanic cell of claim 16,wherein the primary and auxiliary electrode pairs are separated by achemically inert insulating mesh.
 18. The galvanic cell of claim 15,wherein the redox electrolyte pair comprises a gel-type electrolyte. 19.The galvanic cell of claim 15, wherein the anodic electrolyte comprisesa non-aqueous media housed in an anaerobic anode compartment, and thenon-aqueous media comprises a mixture of quinone species.